Please--the term is "tabs", not "taps"! 🙂
And you're not wording properly the preference at the path you describe:
Safari>Preferences>Main window>Select 'open new tap existing window'
You should use the term "General", not "Main window"--this properly identifies which preference category you want to choose, since the "main window"/General category isn't automatically displayed each time you open Preferences--the category that's displayed, is the one that was last selected prior to the Preferences window being closed.
And the specific term shown in the General category, that you're describing, isn't "Open new tap existing window"--it's "Open links from applications: in a new tab in the current window". Obviously it means the same thing that you're saying, but often if you use different words than the actual ones contained in a preferences window, alert box, etc. in replying to someone's question, it can confuse them, and it's easy enough to use the exact wording that's contained in those windows.
Power Mac G4 Mirrored Drive Door, dual 1.25 GHz Mac OS X (10.4.9) 2 gig RAM, two serial ATA drives connected to a FirmTek SeriTek/1VE2+2 card